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Gold Straight from the Mine


#1

Hi, I have been asked to make a ring from a 12.5 gram (nearly half
an ounce) piece of gold the customer got from an Australian gold
mine. I thought I could pour a square bar and hammer it into a
half-round steel swage block for a simple gold ring, or alloy it
with copper and silver to make 18k or something, to make a couple
of rings.

The piece of gold has been melted by someone into a roundish shape
and hammered crudely. This set me off wondering about a few things.
Firstly, it has cracked badly at one part of the edge, where a
small part of the surface is crazed with fine cracks. Hmmm.
Obviously not pure 24k, wouldn’t you agree?

Then I phoned a jeweller friend in Queenstown where in the 1860s
there was (as you all know) one of the world’s biggest gold
strikes, and where today prospectors are still finding gold. Colin
quite often works the local gold. He says the gold I have seems
ranges from about 92% pure to a high of 98% pure. He uses local
gold only if it looks like it’s not pale from mercury.

He melts the gold with the flux recommended by Tim McCreight (p5
The Complete Metalsmith) for gold: powdered charcoal and ammonium
chloride (sal ammoniac), or another, 1 part potassium nitrate
(saltpetre) 2 parts potassium carbonate. The flux I use when
soldering and alloying is a modern industrial ‘easiflo’ powder type
used with silphos, easiflo, and such. I also use phosphorus
deoxidiser in melts and alloying in the form of tily pellets of
copper-phos (85%copper).

What advice do you have for me?

  1. Melt it down with flux a few times?
  2. Melt it down with phosphorus deoxidiser?
  3. Leave it alone, as there might be mercury and other stuff in it?

Looking forward to your combined wisdoms.

Regards
Brian
B r i a n � A d a m J e w e l l e r y E y e w e a r �
@Brian_Adam1 ph/fx +64 9 817 6816 NEW ZEALAND
http://www.adam.co.nz/eyewear/
http://www.adam.co.nz/jewellery/
http://www.adam.co.nz/workshop/ NEXT - Queenstown Mar 1998
http://www.adam.co.nz/ruthbaird/ across the bench from me


#2

What advice do you have for me?

  1. Melt it down with flux a few times?
  2. Melt it down with phosphorus deoxidiser?
  3. Leave it alone, as there might be mercury and other stuff in it?

Brian, as you may know, there has been something of a minor
goldrush here in Scotland and one of my students brought in about
3oz which he had collected over a number of years. The first thing
that we did was to have a sample analysed by the assay office,
which told us how much contaminant that there was and what metal
was contaminating it. This, I would suggest, should be your first
step. I don’t know about the assay/hallmarking system in NZ but
here the Office couldn’t have been more helpful: if you don’t have
the same system, some universities might be able to help. If an
analysis showed mercury, I would STILL consider melting it either
outdoors with the wind behind me (it is a small quantity after
all) or in a fume cupboard, otherwise not at all (mercury vapour
can be absorbed through the skin). If the analysis did not show
mercury, I would continue and make up a workable alloy. The
crazing you describe seems a bit unusual, but even small quantities
of aluminium or the like can make gold unworkable. In the end, we
made slightly higher than 18ct (because it had to be hallmarked, we
erred on the side of safety). In your case, I can’t see much
advantage in deoxidising it: you WANT any foreign metals to
oxidise, so melt it a couple of times with flux and granulate it by
pouring into clean water made SLIGHTLY acidic with sulphuric acid.
I hope that this helps. Yours aye, – Dauvit Alexander, Glasgow,
Scotland.


#3
    Hi, I have been asked to make a ring from a 12.5 gram
(nearly half an ounce) piece of gold the customer got from an
Australian gold mine. 

G’day Brian. A jeweller mate of mine is always having people come
with river gold, usually in dust and tiny nuggets, but some they
melted into crude lumps. They invariably want to have wedders made
from it. His way is not to worry about carat value etc, but he
does reckon Motueka River gold is about 18ct anyway. He simply
melts it and casts it into a simple steel rod-mould, about 4-5mm
dia. He rolls this down in a hand-mill to make strip or
half-round, anneals where necessary, pickles it then turns it into
a ring in the time honoured method, then joins with hard solder.
I’ve done it that way

myself If the piece is very pale (so mercury might be present) he
simply rolls the lump thin, puts it out in his sheltered yard on a
bit of sheet iron over a bunsen burner flame, further sheltered in
a cutaway large tin, and leaves it to cook all morning, or longer.
This should lose just about all the mercury. If you want to test
for the presence of mercury, you’d have to dissolve a little of the
material with aqua regia, then pass hydrogen sulphide gas into the
diluted solution neutralised with ammonia. A crimson mercuric
sulphide (cinnabar) confirms the presence of mercury. In fact,
perhaps a solution of potassium sulphide (liver of sulphur) might
work too. But you knew all that anyway, didn’t you? But Cheers,

        /\
       / /    John Burgess, Nelson, New Zealand
      / /
     / //\    @John_Burgess2
    / / \ \
   / (___) \
  (_________)

#4
simply rolls the lump thin, puts it out in his sheltered yard on a
bit of sheet iron over a bunsen burner flame, further sheltered in
a cutaway large tin, and leaves it to cook all morning, or longer. 
This should lose just about all the mercury.   If you want to test

Hmm, okay… sounds feasible

material with aqua regia, then pass hydrogen sulphide gas into the
diluted  solution neutralised with ammonia. A crimson mercuric
sulphide (cinnabar) confirms the presence of mercury.  In fact,
perhaps a solution of potassium sulphide (liver of sulphur) might
work too. But you knew all that anyway, didn't you?    

No! I did once really really really really want a 'Chemistry Set’
when I was about 8 years old (Greymouth on the West Coast) but I
never did get it!

Thanks, John.
Brian
B r i a n � A d a m J e w e l l e r y E y e w e a r �
@Brian_Adam1 ph/fx +64 9 817 6816 NEW ZEALAND
http://www.adam.co.nz/eyewear/
http://www.adam.co.nz/jewellery/
http://www.adam.co.nz/workshop/ NEXT ONE - Queenstown Mar11 to Mar18 '98
http://www.adam.co.nz/ruthbaird/ across the bench from me


#5
    I did once really really really really want a 'Chemistry
Set' when I was about 8 years old (Greymouth on the West Coast)
but I never did get it!

G’day, Brian; I too really really really wanted a chemistry set
when I was very young, but got a very adamant NO! from my parents…
But I got sixpence a week pocket money, and so I saved it up and
secretly bought one when I was ten - and finished up as Senior
Technical Officer at Vic Uni, 50 odd years later! Incidentally I
got some gold out of the Shotover River at Queenstown but had to
beat a hasty retreat when I was almost eaten alive by monsterous
sandflies! Cheers

        /\
       / /    John Burgess, Nelson, New Zealand (JOAT) (MON)
      / /
     / //\    @John_Burgess2
    / / \ \
   / (___) \
  (_________)

#6

Hi John

All I got out of the Shotover was very, very wet. We took a ride
(?) on the rapids when we were on holiday in Queenstown. Wish I
knew there was gold in them thar waters (g). Great excuse to
return to NZ.

Best.

Linda
@Red1Eagle
New Jersey (northeast) USA